It is a recent tendency to change a mechanical driving system to an electrical driving system, which uses a motor, for meeting requirements to save space, simplify assembling work and enhance controllability in a vehicle. As disclosed in JP 2004-56856A (US 2004/0008002A1 and US 2006/0108966A1), for example, a shift range switchover mechanism of an automatic transmission of a vehicle is driven by a motor. This apparatus uses an encoder, which outputs output signals at each rotation of a predetermined angular interval in synchronization with rotation of the motor, and rotationally drives the motor by sequentially switching over current supply phases of the motor based on a count value of the output signals of the encoder.
It is under development to uses in a control circuit an integrated IC, which includes plural functions such as receiving of the output signals of the encoder and supplying currents to phases of the motor.
When a power source voltage falls to be lower than an operation guarantee voltage of the integrated IC, the integrated IC is disabled to perform its function of receiving the output signals of the encoder and update a count value of the output signals of the encoder. For this reason, it is necessary to detect abnormality of the integrated IC. If the abnormality of the signal receiving function of the integrated IC is not detected, the encoder is likely to be detected as being abnormal and the encoder or an encoder-integrated motor, which is still normal, is likely to be replaced with new one erroneously.
It is therefore an object of the present disclosure to provide a motor control apparatus, which detects abnormality of an integrated IC mounted in a system for rotationally driving a motor by switching over current supply phases based on a count value of output signals of an encoder.
According to one aspect, a motor control apparatus comprises a motor provided as a drive power source for a control object, an encoder for outputting output signals in synchronization with rotation of the motor, a control part for rotationally driving the motor by sequentially switching over a current supply phase of the motor based on a count value of the output signals of the encoder, an integrated IC having plural functions, which include at least one of a receiving function for receiving output signals of the encoder and a power supply function for supplying a current to each phase of the motor, and an abnormality diagnosis part for checking individually whether an abnormality is present potentially with respect to at least two functions among the plural functions of the integrated IC and checking whether the integrated IC is abnormal based on check results about the at least two functions.